Polyorganosiloxane compositions which cure to elastomeric materials at room temperature are well known. Such compositions can be obtained by mixing polydiorganosiloxanes having reactive groups, such as silanol groups, with silane crosslinking agents, for example, alkoxysilanes, acetoxysilanes, oximosilanes, or aminosilanes, and catalysts as necessary. Compositions comprising these ingredients can then be cured by exposure to atmospheric moisture at room temperature.
Moisture curable compositions are well known for their use as sealants. Moisture curable compositions require a significant amount of time, commonly several days, in which to fully cure before reaching maximum strength. In certain applications which utilize sealant in assembly line applications, it is necessary to use a sealant which can rapidly develop green strength. Sealants which rapidly develop green strength have the advantage of allowing the sealant user to handle, package and ship the assembled construction after relatively shorter cure times without damage to the assembled construction, thus increasing production line speed and lowering product inventory. Green strength as defined herein means the strength of the sealant used in an assembled construction before the sealant has fully cured.
The present inventors have unexpectedly determined that RTV silicone compositions comprising about 10 to 95 weight percent based on the total weight of the RTV silicone composition of polydiorganosiloxanes comprising on average at least 1.2 chain terminations per molecule selected from the group consisting of hydroxysilyl groups, alkoxysilyl groups, and multi-alkoxysilyl groups, provided that at least one chain termination per molecule is a multi-alkoxysilyl group rapidly develop green strength upon exposure to moisture.
One objective of this invention is to prepare a RTV silicone composition curable in the presence of moisture with rapid development of green strength.